The present invention relates to RF-driven semiconductor devices and, more particularly, to an RF-driven semiconductor device comprising an RF-driven semiconductor chip, a metal plate having the semiconductor chip die-bonded thereto, and outer leads electrically connected to the signal electrode of the semiconductor chip via bonding wires, all of which are packaged with a mold resin.
At present, an RF-driven semiconductor device wherein a semiconductor chip, a metal plate having the semiconductor chip die-bonded thereto, and outer leads electrically connected to the signal electrode of the semiconductor chip are molded in a resin is the most prevalent because of its cost efficiency and excellent manufacturability.
Conventionally, the RF-driven semiconductor device composed of a plastic mold package has been used in such a device as a television set, a video recorder, or a personal computer which operates at a frequency, at most, of 200 MHz or less.
However, since RF power ranging in frequency from 1 to 2 GHz has been used in terminal equipment for recent mobile communication, provisions should be made for high frequencies in an RF-driven semiconductor device to be mounted on such terminal equipment. The difference in operating frequency between several hundreds of megahertz and several gigahertz exerts two major influences upon the RF-driven semiconductor device: increased inductance that should be reduced by providing a minimum path for the ground potential and a drastic change in impedance caused by increased capacitance and inductance due to the outer leads protruding outwardly from the plastic package.
Because miniaturization and weight reduction are required of the terminal equipment for mobile communication which employs RF power, miniaturization and weight reduction are also required of the RF-driven semiconductor device to be mounted on the terminal equipment. In addition, higher integration of functions is required of the RF-driven semiconductor device.
Higher integration of functions may be achieved by a first method wherein increasing miniaturization is pursued as in recent silicon LSIs or by a second method wherein a plurality of semiconductor chips having different functions and manufactured by different processes are molded in a single plastic package for the achievement of a higher packaging efficiency than is achievable in the case of molding the semiconductor chips in individual plastic packages.
In accordance with the second method, higher integration of functions and further miniaturization are achieved in the terminal equipment for mobile communication than in the case where a plurality of semiconductor chips are molded in individual plastic packages. By thus molding the plurality of semiconductor chips in the single plastic package, the plurality of semiconductor chip manufactured by different processes are enabled to function as a single RF-driven semiconductor device. For example, there has been proposed the technology for molding, in a single package, a modulator IC formed on a silicon substrate and a MOSFET for amplifying RF power formed on a compound semiconductor, each used in the terminal equipment for mobile communication.
Referring now to FIGS. 17(a) to 17(d), a semiconductor device according to a first conventional embodiment will be described. FIGS. 17(a) to 17(d) show the semiconductor device having an RF-driven semiconductor chip, of which FIG. 17(a) is a plan view, FIG. 17(b) is a cross-sectional view taken along the line XVII--XVII of FIG. 17(a), FIG. 17(c) is a front view, and FIG. 17(d) is a bottom view.
As shown in the drawings, the RF-driven semiconductor chip (not shown) is die-bonded to the top face of a metal plate 100 separated from a lead frame. The metal plate 100 and the semiconductor chip are molded together with outer leads 101 for connection with an external electrode, which are also separated from the lead frame, in a plastic package 102 in the form of a flat rectangular parallelepiped. The signal electrode of the semiconductor chip is electrically connected to the outer leads 101 via bonding wires or the like, though the drawing thereof is omitted here. In this case, the outer leads 101 are protruding outwardly from the pair of opposed side faces of the plastic package 102. On the other hand, the metal plate 100 are protruding from the front and rear side faces of the plastic package 102, while having projections 100a bending over to the back face of the plastic package 102. The projections 100a of the metal plate 100 are connected to the ground pattern of a printed circuit board (not shown) for grounding. Countermeasures have thus been taken against increased inductance in the semiconductor device according to the first conventional embodiment.
Referring next to FIGS. 18(a) to 18(d), a semiconductor device according to a second conventional embodiment will be described. FIGS. 18(a) to 18(d) show the semiconductor device having an RF-driven semiconductor chip, of which FIG. 18(a) is a plan view, FIG. 18(b) is a side view, FIG. 18(c) is a front view, and FIG. 18(d) is a bottom view. In the second conventional embodiment, the description of the same components as used in the first conventional embodiment will be omitted by providing the same reference numerals. The second conventional embodiment is different from the first conventional embodiment in that the metal plate 100 has the front, rear, right, and left side faces thoroughly covered with a plastic package 102, except for the center of the back face thereof, which is uncovered with the plastic package 102 to be connected by soldering to the ground pattern of the printed circuit board. Thus, countermeasures have also been taken against higher inductance in the semiconductor device according to the second conventional embodiment.
Referring next to FIGS. 19(a) and 19(b), a semiconductor device according to a third conventional embodiment will be described. FIGS. 19(a) and 19(b) show the semiconductor device having a semiconductor chip driven with low-frequency power, of which FIG. 19(a) is a plan view and FIG. 19(b) is a side view. Since the semiconductor device according to the third conventional embodiment is driven with low-frequency power, it falls into a technical category different from the technical category into which the RF-driven semiconductor device according to the present invention falls. However, the description will be given to the semiconductor device according to the third conventional embodiment because of some common components used in both of the semiconductor devices.
As shown in the drawings, the semiconductor chip (not shown) is die-bonded to the top face of a metal plate 100 separated from a lead frame. The metal plate 100 and the semiconductor chip are molded in a plastic package 102 together with outer leads 101 for connection with an external electrode, which are also separated from the lead frame. The signal electrode of the semiconductor chip is electrically connected to the outer leads 101 via bonding wires or the like, though the drawing thereof is omitted here. The third conventional embodiment is characterized in that the outer leads 101 are protruding only from the front side face of the plastic package 102. The both edge portions of the rear side face of the plastic package 102 are partially cut away so that the metal plate 100 is exposed at the top surface through the cutaway portions 102a. The exposed portions of the metal plate 100 are formed with respective holes 100c. The metal plate 100 and hence the semiconductor device according to the third conventional embodiment are fastened to the printed circuit board with screws inserted into the holes 100c.
Referring next to FIGS. 20(a) and 20(b), a semiconductor device according to a fourth conventional embodiment will be described. FIGS. 20(a) and 20(b) show the semiconductor device having a plurality of, e.g., two RF-driven semiconductor chips, of which FIG. 20(a) is a plan view and FIG. 20(b) is a cross-sectional view taken along the line XX--XX of FIG. 20(a).
As shown in the drawings, first and second RF-driven semiconductor chips 105 and 106 are die-bonded to the top face of a metal plate 100 separated from a lead frame. The metal plate 100 and the first and second semiconductor chips 105 and 106 are molded together with outer leads 101 for connection with an external electrode, which are also separated from the lead frame, in a plastic package 102 in the form of a flat rectangular parallelepiped. The respective signal electrodes of the first and second semiconductor chips 105 and 106 are electrically connected to the outer leads 101 via bonding wires or the like, though the drawing thereof is omitted here. In this case, the outer leads 101 are protruding outwardly from the front and rear side faces of the plastic package 102. On the other hand, the metal plate 100 is protruding from the right and left side faces of the plastic package 102. The first and second semiconductor chips 105 and 106 are die-bonded to the top face of the metal plate 100, while projections 100a of the metal plate 100 are connected to the ground pattern of a printed circuit board (not shown) for grounding. Thus, countermeasures have also been taken against higher inductance and provisions have been made for the achievement of higher integration of functions in the package for RF semiconductor according to the fourth conventional embodiment.
In the semiconductor device according to the first conventional embodiment shown in FIGS. 17(a) to 17(d), grounding for RF power has been achieved by the projections 100a of the metal plate 100 protruding from the plastic package 102 and bending over to the back face thereof, while the package has not been miniaturized satisfactorily. Since each of the projections 100a is normally required to have a length of about 1 mm, the projections 100a on both sides increase the size of the package by about 2 mm in total. If the metal plate 100 is provided with the projections having the total length of 2 mm, the length of the plastic package 102 having an original length of about 5 to 6 mm will be increased substantially by about 40%. The scaling up of the semiconductor device is incompatible with the trends toward further miniaturized terminal equipment for mobile communication. Hence, the implementation of an IC having maximum functions and occupying a minimum area has been demanded strongly for miniaturized terminal equipment.
In the semiconductor device according to the second conventional embodiment shown in FIGS. 18(a) to 18(d), grounding for RF power has been achieved by the metal plate 100 exposed at the center of the back face of the plastic package 102 and the substantial increase in the length of the plastic package 102 can be avoided. However, since the metal plate 100 is soldered to the printed circuit board only at the center of the back face thereof, it is difficult to verify from the outside that the metal plate 100 is soldered after the mounting of the semiconductor device onto the printed circuit board. As a result, the process may proceed to the subsequent step with the metal plate 100 deficiently soldered to the printed circuit board, which leads to a rejection in the final conduction test on account of faulty operation. Thus, although the plastic package 102 can be miniaturized in the second conventional embodiment, the yield of the device is lowered disadvantageously.
In the semiconductor device according to the third conventional embodiment shown in FIGS. 19(a) and 19(b), the outer leads 101 are protruding from the front side face of the plastic package 102 and the metal plate 100 is fastened to the printed circuit board at the both edge portions of the rear side face thereof with small screws. Therefore, the third conventional embodiment is not applicable to a semiconductor device in which a larger number of outer leads are protruding from a small-sized plastic package such as the RF-driven semiconductor device for use in the terminal equipment for mobile communication.
The semiconductor device according to the fourth conventional embodiment shown in FIGS. 20(a) and 20(b) has the following problem. In die-bonding the first and second semiconductor chips 105 and 106 to the metal plate 100, the semiconductor chips are pressed against the metal plate 100 with a bonding material such as a gold-silicon alloy, gold-lead alloy, or silver paste attached to the back faces of the semiconductor chips and the bonding material attached to that one of the first and second semiconductor chips 105 and 106 die-bonded earlier is pushed out of the back side of the semiconductor chip and spreads extensively on the top face of the metal plate 100. The bonding material on the metal plate 100 further spreads out to the region to which the other of the first and second semiconductor chips 105 and 106 is to be die-bonded later. This prevents the semiconductor chip die-bonded later from being placed in parallel with the top surface of the metal plate 100, resulting in unsatisfactory wire bonding between the signal electrode of the semiconductor chip and the outer leads. Although the foregoing problem may be solved by increasing the spacing w between the first and semiconductor chips 105 and 106, the size of the plastic package 102 is also increased disadvantageously. Specifically, it is necessary to adjust the spacing w between the first and second semiconductor chips 105 and 106 to be equal to or more than 0.6 mm in order to prevent the bonding material applied to the semiconductor chip die-bonded earlier from spreading out to the region to which the other semiconductor chip is to be die-bonded later. However, a spacing of 0.6 mm or more may not be provided between the first and second semiconductor chips 105 and 106 in the RF-driven semiconductor device in which a plurality of semiconductor chips are die-bonded to a single metal plate for the miniaturization of the plastic package 102.
As described above, the semiconductor devices according to the first, third, and fourth conventional embodiments are disadvantageous in terms of miniaturizing the plastic packages, while the semiconductor device according to the second conventional embodiment is disadvantageous in terms of reliability and yield.